1. 1. Field of the Invention
The present invention relates to needle assemblies employed in the collection or dispensing of liquid samples and particularly to needle assemblies which provide a visual indication of the presence, within the bore of the needle, of a liquid having a temperature which differs from the local ambient temperature. More specifically, this invention is directed to the sampling of body fluid, for example blood, wherein a visual indication is provided when the sampling needle is in fluid flow communication with a blood vessel or other fluid filled part of the body of an animal. Accordingly, the general objects of the present invention are to provide a novel and improved apparatus and method of such character.
2. Brief Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well-suited for use in the collection of blood from a human patient. The provision of assurance that a blood connecting needle is, prior to an attempt to initiate the collection procedure, in fluid flow communication with a blood vessel constitutes a long-standing problem. In many situations, the nurse or clinician attempting to collect blood, or to administer a pharmaceutical, is uncertain, even with tourniquet pressure applied, whether vein entry has been achieved by the pointed distal end of a needle cannula. In the case of blood collection, if a vein is not penetrated, or if the needle passes completely through a thin vein, the nurse or clinician will have to search for a new vein. This is most uncomfortable for the patient and, where evacuated collection tubes are employed, often results in the evacuated tube losing its vacuum, thus requiring that a new evacuated tube be mated to the needle assembly. Many attempts to solve this problem, none of which have achieved widespread acceptance among the medical professionals, have been proposed.
For an example of state-of-the-art blood withdrawing devices which employ an evacuated collecting tube, reference may be had to U.S. Pat. Nos. 3,886,930 and 4,079,729. In the use of these patented devices, vein penetration is indicated when the evacuated tube and needle assembly are pushed together, thereby establishing fluid communication between the interior of the evacuated tube and the needle bore, by the flow of blood into the evacuated tube. Obviously, if blood does not enter the evacuated tube, vein penetration has not been achieved and the needle will have to be withdrawn and relocated.
In an attempt to reduce patient discomfort and a waste of evacuated collecting tubes, various vein locating indicators have been proposed. In one class of such indicators, a needle assembly is provided with a transparent chamber and the entry of blood into this chamber, prior to the joining of the evacuated tube to the needle assembly, will provide an indication of vein penetration. For examples of this approach, reference may be had to U.S. Pat. Nos. 3,585,984; 4,166,450; 4,436,098; 4 416,290; and 4,312,362. A major deficiency with this approach s that it adds significantly to cost of manufacture of the needle assembly and presents the possibility of a false indication, i.e., the failure of the chamber to fill may simply be a result of insufficient pressure differential, an air lock or a defective collection device. The added cost results from the fact that the needle assemblies require either a complex valving system and/or a chamber having an air permeable wall or membrane. Further, to be practical, needle assemblies of the type being discussed require the presence of a relatively large quantity of aspirated blood in order to permit the visual confirmation of vein penetration. The transfer of this quantity of blood into the indicator chamber, without a driving negative pressure mechanism such as an evacuated tube, presents a problem if an air-lock develops within the needle assembly or if the patient has a "weak" vein. Obviously, if the operator does not see aspirated blood in the indicator chamber, it may be incorrectly concluded that a vein has not been penetrated, thus leading to unnecessary and painful vein searching.
It is to be noted that use of transparent blood collecting chambers to indicate vein penetration has also been proposed for I.V. catheters. As an example of this technology, reference may be had to U.S. Pat. No. 4,108,175 wherein the added complication of mechanical means to create a negative pressure to draw blood into the transparent chamber is provided. The comments above with respect to the deficiencies of needles having transparent indicator chambers are generally applicable to catheters.
It has also been suggested that local tissue temperature can be measured and employed to position a fluid withdrawing device. For example, referring to U.S. Pat. No. 4,280,508, it has been proposed to employ a temperature sensing probe, located inside of the needle bore, which is removed from the needle assembly after positioning but prior to fluid withdrawal. The patented device is disclosed as being used in an amniocentesis procedure. Other suggestions for the use of a temperature probe within the bore of a needle, coupled with transmission of a signal commensurate with the sensed temperature to a remote location, may be seen from U.S. Pat. Nos. 4,476,877 and 4,665,927.
It has also been proposed to locate superficial and sub-superficial veins, for subsequent venipuncture, by sensing the temperature on the surface of a patient's skin. Thus, U.S. Pat. Nos. 4,015,591; 4,175,543 and 4,448,204 relate to the use of thermochromic liquid crystal mixtures which are applied to the patient's skin. In theory, the surface of the skin above a vein would be warmer than the surrounding tissue and this the vein pattern would be reflected by the color pattern observed in the liquid crystal containing coating which is in contact with the skin. In actual practice, however, this technique works only where the patient's veins are sufficiently large and close to the skin surface that the nurse or clinician can likely find and penetrate the vein without the liquid crystal "map".